DNA
Deoxyribonucleic Acid
Dr. Jim Bidlack
University of Central Oklahoma
jbidlack@ucok.edu
http://biology.ucok.edu/bidlack
Special thanks to John Wilson for providing the template of this presentation in partial
fulfillment for Cell Physiology (BIO 4454) during the Fall 2002 Semester.
History of DNA
 Fred Griffith and the mouse experiment
 Transforming
“principle”
 Oswald Avery’s conclusion of DNA as
the transforming principle
 Isolation
of DNA
 Watson & Crick’s Double Helix
 Sugar,
phosphate, base
Structure of DNA
 DNA is a double helix
made of complimentary
antiparallel strands
 The backbone is
constructed of a five
carbon sugar and a
phosphate group
 The rungs consist of the
different bases held
together by hydrogen
bonds
Structure of Nucleic Acids
 DNA is a five carbon
sugar with two
hydrogens on the
second carbon
 RNA is a five carbon
sugar with a
hydrogen and
hydroxyl group on
the second carbon
Structure of the DNA Bases
 Two classes of bases:
Purines and
Pyrimidines
 Purines consist of
Adenine (A) and
Guanine (G)
 Pyrimidines consist of
Thymine (T) and
Cytosine (C)
 Bases are the same in
RNA except that Uracil
(U) is substituted for
Thymine
Backbone Linkage
 Any nucleotide can be




connected with a
phosphodiester bond
Nucleotides are
triphosphated
The 5’ ends with a
phosphate and the 3’
ends with a hydroxyl
The phosphate is
attached to the 5’
carbon and the 3’
carbon of the sugar
The bases are attached
to the first carbon
DNA Linkage
 Helix is anti-parallel and




complimentary
Left side is from 5’ end
to 3’ end
Right side is from 3’ end
to 5’ end
A matches with T
stabilized by two
hydrogen bonds
C matches with G
stabilized by three
hydrogen bonds
DNA Replication
 Replication is semi-
conservative
 Each strand is a
template for another
strand
 New DNA strands
contain one new strand
and one parental strand
 Bases on strands are
complimentary (A w/ T
& C w/ G)
DNA Replication
 DNA synthesizes in one direction, from the 5’
end to the 3’ OH end
 Many enzymes contribute in the replication of
DNA

Helicases - unwind the DNA
 Topoisomerases - releases the tension
 Single Stranded Binding Proteins - maintain the
single strands after unwinding
 DNA polymerases - add nucleotides and reads the
template strand. There are five polymerases for
mammals. Must have a 3’ OH end
Summary
 DNA is a double helix with complementary




anti-parallel strands
DNA consists of sugar, phosphate and bases
There are two classes of bases: Purines and
Pyrimidines
Nucleotides are connected by a
phosphodiester bond
Replication is semi-conservative from the 5’
end to the 3’ end and involves several
enzymes